OLED display having thermally conductive material

ABSTRACT

An OLED device comprising: a) a substrate; b) one or more OLED light emitting elements located on the substrate and including a first electrode formed on the substrate, one or more OLED light emissive layers located over the first electrode, and a second electrode located over the OLED light emissive layers; c) an encapsulating cover located over the second electrode and affixed to the substrate; and d) a thermally-conductive, conformable, and compressible material in thermal contact with both the OLED light emitting elements and the encapsulating cover over the light emitting area of the OLED light emitting elements, wherein the thermally-conductive material is more than 1 micron thick and has a thermal conductivity greater than 0.25 W/mK.

FIELD OF THE INVENTION

The present invention relates to organic light-emitting diode devices.In particular, the present invention relates to improving devicelifetime and reducing localized non-uniformity in an OLED device due toheating within an organic light-emitting display device.

BACKGROUND OF THE INVENTION

Organic light-emitting diode (OLED) display devices typically include asubstrate having one or more OLED light-emitting elements including afirst electrode formed thereon, one or more OLED light-emitting layerslocated over the first electrode, and a second electrode located overthe OLED light-emitting layers, and an encapsulating cover located overthe second electrode, affixed to the substrate, and forming a cavitybetween the inside of the encapsulating cover and the second electrode.Such an OLED device may be top-emitting, where the light-emittingelements are intended to emit through the cover, and/or bottom-emitting,where the light-emitting elements are intended to emit through thesubstrate. Accordingly, in the case of a bottom-emitting OLED device,the substrate and first electrode must be largely transparent, and inthe case of a top-emitting OLED device, the cover and second electrodemust be largely transparent.

Referring to FIG. 3, a top-emitter OLED device discussed in the priorart includes a substrate 10 on which is deposited one or more firstelectrodes 20 separated by insulators 28, one or more organic layers 22comprising the OLED (at least one of which is emissive when a current ispassed through the layers) and a second, common electrode 24. Anencapsulating cover 12 is affixed to the substrate 10 and seals theorganic layers 22 from the environment. A cavity 14 exists between thesecond electrode 24 and the cover 12 and is usually filled with an inertgas. This cavity is typically from 10 microns to 50 microns wide, muchthicker than a typical thin-film layer in an OLED device. Desiccantmaterials designed to protect the OLED materials may be located in thecavity, either above the light emissive area in the OLED device oraround the periphery of the light emissive area in the OLED device.Thin-film protective layers (not shown) may also be deposited over thesecond electrode 24 and are employed to protect the second electrode 24.In this top-emitter configuration, light 26 is emitted through the coverso that the cover 12 and second electrode 24 must be transparent whilethe substrate 10 and the electrode 20 may be opaque or reflective.

Referring to FIG. 4, a commercially available bottom-emitter OLED deviceincludes a substrate 10 on which is deposited one or more firstelectrodes 20, one or more organic layers 22 (at least one of which isemissive when a current is passed through the layers) and a second,common electrode 24. A cover 12 is affixed to the substrate and sealsthe OLED materials from the environment. A cavity 14 exists between thesecond electrode 24 and the cover 12 and is usually filled with an inertgas and may include desiccant materials. In this bottom-emitterconfiguration, light 26 is emitted through the substrate 10 so that thesubstrate 10 and first electrode 20 must be transparent while the cover12 and the second electrode 24 may be opaque or reflective.

A variety of materials may be used to construct suitable substrates andencapsulating covers for OLED devices and to fill the cavity between thesecond electrode and the cover. The desirable material properties and/orcharacteristics of an OLED substrate and cover include low cost, veryflat surface, low coefficient of thermal expansion (CTE), high strengthand stability under a variety of environmental stresses, andelectrically non-conductive (or able to be coated with electricallynon-conductive material). The material used most often for suchsubstrates is glass, typically borosilicate glass, because it istransparent, very stable, can be made at low-cost, and has a very smoothsurface suitable for the deposition and processing of semiconductor andorganic materials. Other substrate materials have been described in theart, for example ceramics, plastics, and metals such as stainless steel(see U.S. Pat. No. 6,641,933 B1 to Yamazaki et al entitled“Light-emitting EL display device”). Because the OLED materials are verysensitive to moisture, the cavity between the second electrode and thecover is often provided with desiccant materials and the cover iscarefully sealed to the substrate (see, e.g., US 20030203700 A1 entitled“Encapsulating OLED devices with transparent cover” by Clark published20031030). Inert gases may be employed to fill the cavity;alternatively, it is known to provide polymer material to fill thecavity (see, for example, US 20030143423 A1 entitled “Encapsulation oforganic electronic devices using adsorbent loaded adhesives” byMcCormick, et al published 20030731).

JP 10-275681 discloses an organic electroluminescent light source havinga light emitting element with a relatively thick cathode and asurrounding conforming protecting resin layer to provide high heatconductivity. However, as described for this arrangement, there is nodisclosure of use of a compressible layer to transfer heat between aseparate encapsulating cover and the organic electroluminescent lightsource. The use of conforming resin protection layer, moreover,typically is inadequate itself to provide desired environmentalprotection to the organic electroluminescent materials. Further, thereis no disclosure of the need to spread heat between an active lightemitting element and an inactive light emitting element in a devicecomprising a plurality of light emitting elements, in order to reducedifferential aging of such light emitting elements.

Organic light-emitting diodes can generate efficient, high-brightnessdisplays. However, heat generated during the operation of the display inhigh-brightness modes can limit the lifetime of the display, since thelight-emitting materials within an OLED display degrade more rapidlywhen used at higher temperatures. While it is important to maintain theoverall brightness of an OLED display, it is even more important toavoid localized degradation within a display. The human visual system isacutely sensitive to differences in brightness in a display. Hence,differences in uniformity are readily noticed by a user. Such localizeddifferences in uniformity in an OLED display may occur as a consequenceof displaying static patterns on the display, for example, graphic userinterfaces often display bright icons in a static location. Such localpatterns will not only cause local aging in an OLED display, but willalso create local hot spots in the display, further degrading thelight-emitting elements in the local pattern. Glass and plasticsupports, the use of which is advantageous in view of their relativeelectrical non-conductivity, may not be sufficiently thermallyconductive to provide a uniform temperature across the substrate whenthe display is in operation. Hence, improved thermal managementtechniques may significantly improve the life expectancy of an organicdisplay device.

One method of removing heat from an organic light emitting displaydevice is described in U.S. Pat. No. 6,265,820, entitled, “Heat removalsystem for use in organic light emitting diode displays having highbrightness.” The '820 patent describes a heat removal system for use inorganic light emitting diode displays. The heat removal assemblyincludes a heat dissipating assembly for dissipating heat from theorganic light emitting device, a heat transfer assembly for transferringheat from the top organic light emitting device to the heat dissipatingassembly and a cooling assembly for cooling the organic light emittingdisplay device. While the system of the '820 patent in one embodimentprovides a thermally conductive intermediate material positioned betweenthe organic light emitting device and a sealed backplate, the use ofspecific materials suggested (metallic layers or non-metallic thermalpaste) do not provide mechanical flexibility or are difficult toassemble in OLED devices. Moreover, the structure described in the '820patent is complex, requiring multiple layers.

U.S. Pat. No. 6,480,389 to Shie et al entitled “Heat dissipationstructure for solid-state light emitting device package” describes aheat dissipation structure for cooling inorganic LEDs and characterizedby having a heat dissipating fluidic coolant filled in a hermeticallysealed housing where at least one LED chip mounted on a metallicsubstrate within a metallic wall erected from the metallic substrate.Such an arrangement is complex, requires fluids, and is not suitable forarea emitters such as OLEDs.

US 2004/0004436 A1 entitled “Electroluminescent display device” byYoneda published Jan. 8, 2004, describes an organic EL panel having adevice glass substrate provided with an organic EL element on a surfacethereof, a sealing glass substrate attached to the device glasssubstrate, a desiccant layer formed on a surface of the sealing glasssubstrate, and noncompressible (e.g., metal) spacers disposed between acathode of the organic EL element and a desiccant layer. Aheat-conductive layer can be formed by vapor-depositing or sputtering ametal layer such as a Cr layer or an Al layer that inhibits damaging theorganic EL element and increases a heat dissipating ability, therebyinhibiting aging caused by heat.

U.S. Pat. No. 6,633,123 B2 entitled “Organic electroluminescence devicewith an improved heat radiation structure” issued 20031014 provides anorganic electroluminescence device including a base structure and atleast an organic electroluminescence device structure over the basestructure, wherein the base structure includes a substrate made of aplastic material, and at least a heat radiation layer which is higher inheat conductivity than the substrate.

U.S. Pat. No. 5,821,692 A entitled “Organic electroluminescent devicehermetic encapsulation package” issued 19981013 describes an organicelectroluminescent device array encapsulating package including anorganic electroluminescent device on a supporting substrate. A coverhaving a rim engaging the supporting substrate is spaced from andhermetically encloses the organic electroluminescent device. Adielectric liquid having benign chemical properties fills the spacebetween the cover and the organic electroluminescent device, providingboth an efficient medium for heat transmission and an effective barrierto oxygen and moisture. Similalry, JP11195484 A entitled “Organic ELElement” by Yasukawa et al. published 19990721 describes an organic ELelement equipped with an organic EL structural body laminated on asubstrate, and a sealing plate arranged on the organic EL structuralbody with a predetermined gap, where a sealing substance having heatconductivity of 1.1×10⁻¹ W.m⁻¹.K⁻¹ or more, and viscosity of 0.5 to 200cP at 25° C. is filled in the sealed space. While such dielectricliquids can be useful, applicant's experience with such materials isthat they are difficult to use in manufacturing. Moreover, if the OLEDdevice and package are compressed, the incompressible liquid will putstress on the OLED layers and packaging of the device.

JP2003100447 A entitled “Organic Electroluminescence Equipment” byHashimoto et al. published 20030404 describes a high sealing resin layerand a high heat-conductivity resin layer formed in the gap of a glasssubstrate and a sealing substrate in the perimeter part of the sealingsubstrate. Such a layer does not assist in removing or spreading heatfrom the emissive areas of the OLED device.

Heat sinks are also well known in the integrated circuit industry andare applied to cooling large integrated circuits. Such sinks typicallyare thick and are unsuitable for displays in which limiting thethickness of the display is an important goal. Moreover, heat sinks donot improve the thermal conductivity of an OLED device itself.

It is therefore an object of the present invention to provide a moreuniform distribution of heat within an OLED display and to improve theremoval of heat from an OLED display device thereby increasing thelifetime of the display.

SUMMARY OF THE INVENTION

In accordance with one embodiment, the invention is directed towards anOLED device comprising:

a) a substrate;

b) one or more OLED light emitting elements located on the substrate andincluding a first electrode formed on the substrate, one or more OLEDlight emissive layers located over the first electrode, and a secondelectrode located over the OLED light emissive layers;

c) an encapsulating cover located over the second electrode and affixedto the substrate; and

d) a thermally-conductive, conformable, and compressible material inthermal contact with both the OLED light emitting elements and theencapsulating cover over the light emitting area of the OLED lightemitting elements, wherein the thermally-conductive material is morethan 1 micron thick and has a thermal conductivity greater than 0.25W/mK.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a top-emitting OLED device according toone embodiment of the present invention;

FIG. 2 is a schematic diagram of a bottom-emitting OLED device accordingto an embodiment of the present invention;

FIG. 3 is a prior-art schematic diagram of a top-emitting OLED device;

FIG. 4 is a prior-art schematic diagram of a bottom-emitting OLEDdevice;

FIG. 5 is a diagram illustrating the heat flow of a top-emitting OLEDdisplay as shown in FIG. 3;

FIG. 6 is a diagram illustrating the heat flow of an OLED deviceaccording to an embodiment of the present invention;

FIG. 7 is a schematic diagram of a top-emitting OLED device according toan alternative embodiment of the present invention;

FIG. 8 is a schematic diagram of a bottom-emitting OLED device accordingto an alternative embodiment of the present invention;

FIG. 9 is a schematic diagram of a bottom-emitting OLED device accordingto an alternative embodiment of the present invention; and

FIG. 10 is a diagram illustrating the heat flow of an OLED deviceaccording to an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a top-emitter embodiment of the present inventionincludes a substrate 10 on which is deposited OLED light-emittingelements comprising first electrodes 20 separated by insulators 28, oneor more organic layers 22 (at least one of which is emissive when acurrent is passed through the layers) and a second, common electrode 24.A cover 12 is affixed to the substrate and seals the OLED materials fromthe environment. A thermally conductive, conformable, and compressiblematerial 16 is located in thermal contact with the second electrode 24of the light-emitting elements and the encapsulating cover 12. Acompressible material used in accordance with the invention is one thatoccupies a given volume when not stressed, and occupies a smaller volumewhen placed under mechanical stress. The thermally conductive materialhas a conductivity greater than 0.25 W/mK, more preferably greater thanor equal to 1.0, and a thickness of greater than 1 micron, i.e. thethermally conductive material is not a thin-film and preferably fillsthe cavity between the second electrode 24 and the cover 12. Secondelectrode 24 may comprise a single conductive layer, or may comprisemultiple conductive layers or a combination of conductive and protectivelayers. Thermal contact between the thermally conductive material andthe light-emitting elements and cover is established when heat flowsreadily between the thermally conductive material and the OLEDlight-emitting elements and the cover over the entire light emittingarea of the OLED light-emitting elements. In the top-emitterconfiguration shown in FIG. 1, light 26 is emitted through the cover sothat the cover 12, second electrode 24, and the thermally conductivematerial 16 must be transparent while the substrate 10 and the electrode20 may be opaque or reflective.

Referring to FIG. 2, a complementary bottom-emitter embodiment of thepresent invention includes a substrate 10 on which is deposited OLEDlight-emitting elements comprising first electrodes 20, one or moreorganic layers 22 (at least one of which is emissive when a current ispassed through the layers) and a second, common electrode 24. A cover 12is affixed to the substrate and seals the OLED materials from theenvironment. A thermally conductive, conformable, and compressiblematerial 16 is in thermal contact with the second electrode 24 of thelight-emitting elements and the cover 12. In this bottom-emitterconfiguration, light is emitted through the substrate 10 so that thesubstrate 10 and first electrode 20 must be transparent while the cover12, the second electrode 24, and the thermally conductive material 16may be opaque or reflective.

In a particular embodiment, the OLED device may include a plurality ofOLED light emitting elements located on the substrate, where each lightemitting element includes a first patterned electrode formed over thesubstrate and one or more OLED light emissive layers located over thefirst electrode, and a second electrode layer located over the pluralityof OLED light emitting elements. In such embodiment, there willtypically be a patterned insulating layer between the patternedelectrodes. Where a plurality of OLED elements are present, thethermally conductive material preferably has a continuous thicknessgreater than 1 micron over and between the plurality of light emittingelements, to facilitate spreading of heat from an active element to aninactive element.

The thermally conductive material 16 may be any compressible materialconformable to the cavity 14 (shown in FIGS. 3 and 4), for example,polymers and silicones, and having a thermal conductivity greater than0.25 W/mK and a thickness greater than 1 micron. Conventionalcompressible polymers with a thermal conductivity of 0.25 W/mK or lessare not suitable when used alone, while composite conductive materialsmade of a compressible first polymer with the addition of a heatconducting second material having a thermal conductivity greater thanthat of the polymer may provide an overall effective thermalconductivity of greater than 0.25 W/mK are suitable. Additives such asmetallic or ceramic particles and nano-materials including metallic orcarbon components may be employed. Alternatively, thermally conductivecompressible polymers may be employed, for example, Gap Pad materialhaving a thermal conductivity of 2.0 W/mK commercially available fromThe Bergquist Company. Additional thermally conductive pads having athermal conductivities of 2.3 W/mK to 5.0 W/mK are also available fromThe Bergquist and 3M companies. Silicone materials are also useful, forexample, Sil Pad material having a thermal conductivity of 1.3 W/mKcommercially available from The Bergquist Company.

The thermally conductive material may be a compressible, flexible solid.Compressible gels may be employed. Preferably, the material fills thecavity between the light-emitting elements and the cover at least overthe light-emitting area of the OLED device. Thermally conductivematerials can be applied in liquid form and may be cured to form athermally conductive, conformable, compressible solid. Liquidapplication has the advantage that a liquid readily conforms to thevolume and shape needed.

In operation, OLED devices are provided with a voltage differentialacross the electrodes by an external power supply (not shown). Thevoltage differential causes a current to flow through the OLED materialscausing the OLED materials to emit light. However, the conversion ofcurrent to light is relatively inefficient, so that much of the energyis converted to heat. Moreover, much of the emitted light does notescape from the OLED device and is reabsorbed into the device as heat.Hence, OLED devices can become very hot and operate at temperatures wellin excess of ambient temperatures. For example, in an ambientenvironment of 20° C., applicants have demonstrated that an OLED mayoperate at 40° C. to 60° C. or even, at very high brightnesses, inexcess of 100° C. This heat is detrimental to the OLED device. As iswell known, OLED materials degrade as they are used and degrade fasterat higher temperatures. Therefore, providing improved heat management tocool an OLED device improves the lifetime of the OLED device.

In a conventional, prior-art OLED device (as shown in FIGS. 3 and 4),the heat generated within the OLED layers 22 must pass through theelectrodes before it can escape from the OLED device. Some of the heatcan pass through the first electrode 20 and thence through the substrate10 while some of the heat passes through the second electrode 24, thecavity 14, and the encapsulating cover 12. The thermal conductivity ofthe cavity 14 may be 0.025 W/mK (if filled with air) or 0.25 W/mK forconventional polymeric materials as described in the prior art. If acommon epoxy adhesive is used, the thermal conductivity may also be 0.2W/mK. All of these materials represent a significant thermal barrier toheat escaping through the cover 12. The second electrode 24 is typicallymade of metal (for example silver or aluminum) or a metal oxide (forexample, indium tin oxide) or metal alloys. These electrode materialsare relatively good conductors of heat. Unfortunately, the electrodesare typically thin films, for example 2–200 nm thick. Applicant hasdemonstrated that such thin films of metals do not provide adequate heatconductivity.

Referring to FIG. 5, a thermal model of the prior-art OLED shown in FIG.3 is illustrated. In this structure, as shown in FIG. 3, a transparentglass substrate 22 (700 microns thick) is encapsulated by a glass cover12 (also 700 microns thick). A 50-micron air-filled cavity 14 isprovided to simulate the cavity which may be present in OLED devicesbetween the second electrode 24 and the encapsulating cover 12. Energyis applied to a single point 50 on the transparent substrate 10. Theapplied energy raises the temperature of the point to 60° C. Similarlyshaded areas in FIG. 5 represent areas within a band of the sameapproximate temperature. At the opposite end of the substrate and cover,a temperature band 52 has a temperature of 37° C.

As illustrated in FIG. 6, the use of a 50-micron layer of thermallyconductive material 16 in place of air gap 14 significantly reduces theheat, and hence the aging, of the OLED device at point 50. In this case,the thermally conductive material is 3M 5509, a thermally conductive,compressible material having a thermal conductivity of 5.0 W/mK. As canbe seen from this model, the temperature at point 50 is reduced to 48.8°C. Applicants have tested a wide variety of thermally conductive,compressible materials in the cavity 14, and an increase in lifetimeresulting from improved heat removal has been demonstrated.

The heat conductive materials 16 may include desiccant materials and mayalso provide environmental protection to the OLED device, particularlyfrom moisture. Moreover, it is helpful if the heat conductive materials16 is selected to have a coefficient of thermal expansion that ismatched to the cover 12, substrate 10, or the OLED materials 22 orelectrodes 20 and 24. The compressibility of the heat conductivematerials 16 advantageously provides some flexibility to reduce stressfrom differential thermal expansion in the OLED device.

According to the present invention, the substrate 10 or cover 12 may beeither rigid or flexible. Suitably thin layers of either metals orglasses may be used for the substrate or cover. In particular, flexibleplastics may be employed. Since flexible plastic materials do noteffectively seal an OLED display from environmental gases or liquids,the thermally conductive material 16 may provide additional protectionto the OLED display from the environment. Because the thermallyconductive material is compressible, stresses applied to the OLEDdevice, particularly for flexible displays, are accommodated withoutstressing the OLED layers, electrodes, or encapsulation mechanism. Theconformability of the thermally conductive material is important toprovide good thermal contact to both the light-emitting elements and thecover. Moreover, applicants have discovered through experimentation thata flexible material in the cavity may reduce shorts in the OLED layers.

Referring to FIGS. 7 and 8 in top- and bottom-emitter configurationsrespectively, additional heat conductive coatings 30 may be employed onthe outside of the substrate or cover to further conduct heat away fromthe OLED materials 14. Suitable coatings include metals, for example100-micron coatings of Al. Referring to FIG. 9, thin-film heatconductive layers 30 may also be employed on top of the second electrode24, as shown, or on the inside of the cover 12 (not shown). However,such layers are typically much less than 1 micron thick, do not fill thecavity between the second electrode and the cover, and are not inthermal contact with both the second electrode 24 of the light-emittingelements and the cover 12. FIG. 10, illustrates the improvement that maybe obtained by employing an additional thermally conductive layer on theoutside of the encapsulating cover. Referring to FIG. 10, the additionof a 100-micron thick thermally conductive layer 30 of aluminum andusing the same thermally conductive material as in FIG. 6 reduces thetemperature of point 50 to 33° C.

Heat may additionally be removed from the OLED display of the presentinvention by using conventional heat-sinks in thermal contact with anyexternal layers, for example by locating such heat sinks on the outsideof the substrate (for top-emitter OLEDs) or the outside of the cover(for bottom-emitter OLEDs) either in the center of the OLED device or atthe edges. When used within an appliance, the appliance may be placed inthermal contact with OLED device, especially in combination with the useof thermally conductive layers on the outside of the OLED device asdescribed above.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

Accordingly, the preferred embodiments of the invention as described inreference to FIGS. 1, 2, 7, 8, and 9 are intended to be illustrative,not limiting.

PARTS LIST

-   10 substrate-   12 encapsulating cover-   14 cavity-   16 heat conductive material-   20 first electrode-   22 OLED layers-   24 second electrode-   26 light-   28 insulator-   30 heat conductive coating-   50 energy application point-   52 temperature band

1. An OLED device comprising: a) a substrate; b) one or more OLED lightemitting elements located on the substrate and including a firstelectrode formed on the substrate, one or more OLED light emissivelayers located over the first electrode, and a second electrode locatedover the OLED light emissive layers; c) an encapsulating cover locatedover the second electrode and affixed to the substrate; and d) athermally-conductive, conformable, and compressible material in thermalcontact with both the OLED light emitting elements and the encapsulatingcover over the light emitting area of the OLED light emitting elements,wherein the thermally-conductive material is more than 1 micron thickand has a thermal conductivity greater than 0.25 W/mK.
 2. The OLEDdevice claimed in claim 1 wherein the thermally-conductive material is apolymer.
 3. The OLED device claimed in claim 1 wherein thethermally-conductive material is a silicone.
 4. The OLED device claimedin claim 1 wherein the thermally-conductive material is transparent. 5.The OLED device claimed in claim 1 wherein the thermally-conductivematerial has desiccating properties.
 6. The OLED device claimed in claim1 wherein the thermally-conductive material includes a compressiblefirst material and particles of a thermally-conductive second materialdistributed through the first material and having a thermal conductivityhigher than the thermal conductivity of the first material.
 7. The OLEDdevice claimed in claim 6 wherein the thermally-conductive secondmaterial comprises a metal, a metal alloy, a glass, or a ceramic.
 8. TheOLED device claimed in claim 6 wherein the thermally-conductive secondmaterial includes nano-particles.
 9. The OLED device claimed in claim 6wherein the first material is a polymer and the thermally-conductivesecond material is a glass.
 10. The OLED device claimed in claim 9wherein the glass particles are glass beads.
 11. The OLED device claimedin claim 1 wherein the thermally-conductive material has a coefficientof thermal expansion matched to the cover of the device.
 12. The OLEDdevice claimed in claim 1 wherein the thermally-conductive material isdeposited as a liquid and is cured to form a compressible solid.
 13. TheOLED device claimed in claim 1 wherein the thermally-conductive materialis a gel.
 14. The OLED device claimed in claim 1 wherein the OLED deviceis a top-emitting device and the cover and thermally-conductive materialare transparent.
 15. The OLED device claimed in claim 14 wherein thesubstrate has a thermal conductor located on the substrate on the sideof the substrate opposite the OLED light emitting elements.
 16. The OLEDdevice claimed in claim 1 wherein the OLED device is a bottom-emittingdevice and the substrate is transparent.
 17. The OLED device claimed inclaim 16 wherein the encapsulating cover has a thermal conductor locatedon the inside of the cover.
 18. The OLED device claimed in claim 16wherein the encapsulating cover has a thermal conductor located on theoutside of the cover.
 19. The OLED display claimed in claim 1 whereinthe thermally-conductive material is flexible.
 20. The OLED displayclaimed in claim 1 wherein the substrate or cover is flexible.
 21. TheOLED display claimed in claim 1 wherein the thermally-conductivematerial acts as a barrier layer to prevent the passage of gas orliquids through the material.
 22. The OLED display claimed in claim 1wherein the thermally-conductive material fills the space between theencapsulating cover and the OLED light-emitting elements.
 23. The OLEDdisplay claimed in claim 1 wherein the OLED light-emitting elementsfurther comprise protective or conductive layers located on the secondelectrode.
 24. The OLED display claimed in claim 1 wherein thethermally-conductive material has a thermal conductivity greater than1.0 W/mK.
 25. The OLED device claimed in claim 1 comprising a pluralityof OLED light emitting elements located on the substrate, where eachlight emitting element includes a first patterned electrode formed overthe substrate and one or more OLED light emissive layers located overthe first electrode, and a second electrode layer located over theplurality of OLED light emitting elements, wherein the thermallyconductive material has a continuous thickness greater than 1 micronover and between the plurality of light emitting elements.